1. Field of the Invention
The present invention relates generally to an antenna, and more particularly to a dual-patch antenna.
2. Description of the Prior Art
In recent years, Wireless Local Area Network(WLAN) products under IEEE 802.11b/g standard, such as WLAN cards for computers are gaining popularity in wireless communication market. These cards benefit from high gain antennas. In many cases, patch antennas are used.
As well known, a patch antenna usually utilizes a planar conductive patch disposed parallel to a big ground portion and separated from the ground portion by a thin dielectric layer. A feed point is provided to communicate electromagnetic energy to or from the patch. Antennas of this nature may be inexpensively manufactured and may be readily formed into low cost, light weighted phased antenna systems. A typical traditional patch antenna of this case is disclosed in U.S. Pat. No. 5,734,350. Though the traditional patch antenna has much advantage mentioned above, a drawback is that it has a big ground portion resulting in a large size of the antenna. Another drawback is that the radiating pattern of the traditional patch antenna is not omni-direction, thus the scope of the use of the traditional antennas is limited.
As to other type prior arts different from the above one, a family of dual-patch antennas is disclosed in U.S. Pat. No. 4,151,531. The typical antenna of the prior art comprises a dielectric substrate and two electrically conducting rectangular shape elements formed on both sides of the dielectric substrate. The element on one side of the substrate is the mirror image of the element on the other side of the substrate. Each of the elements acts, in effect as a ground portion for the other. The antenna has much smaller size because the antenna does not have a very big absolute ground portion. Additionally, the antenna has good radiating pattern of omni-direction. However, there are some difficulties with the dual-patch antenna. First, the input impedance of the antenna is tuned by varying the location of the feed point, which cannot obtain excellent efficiency. Second, the bandwidth of the antenna is narrow. Usually, to increase the bandwidth of a patch antenna, the thickness of the dielectric substrate is increased, which easily results in impedance mismatching between the antenna and its feeding cable. For an antenna design, impedance matching is one of the most important factors. The impedance mismatching causes a portion of the feed power to be reflected to the signal source rather than to be radiated to the free space. The greater this reflected feed power, the less power that is radiated from the antenna, thus reducing the gain of the patch antenna. So the gain of the patch antenna is sacrificed to achieve wider bandwidth in such resolution. Third, the dielectric substrate of the traditional patch antenna will introduce insertion loss, which does not fit a high gain application.
Hence, in this art, a dual-patch air parch antenna with high performance, simple structure and low cost to overcome the above-mentioned disadvantages of the prior art will be described in detail in the following embodiments.